The present invention relates generally to the field of cell growth laboratory ware and more specifically to a method of treating the surface of a polymer in order to create a product that facilitates cell growth. An apparatus for performing the surface treatment is also provided by the present invention.
The cultivation of living cells is a key component in, among other things, the drug discovery process. Many devices are sold for purposes of cell culture including roller bottles, flasks, dishes, well plates, cell harvesting units, etc. Typically these items of laboratory ware are molded from polymers having a sufficient mechanical stability and strength to create the necessary substrate surface for cell attachment and growth.
Generally, cell growth containers or substrates need to be surface treated after molding in order to make the surface hydrophilic and to enhance the likelihood for effective cell attachment. Surface treatment may take the form of a surface coating, but typically involves the use of directed energy at the substrate surface with the intention of generating chemical groups on the polymer surface. These chemical groups will have a general affinity for water or otherwise exhibit sufficient polarity to permit stable adsorption to another polar group. These functional groups lead to hydrophilicity and or an increase in surface oxygen and are properties recognized to enhance cell growth. Such chemical groups include groups such as amines, amides, carbonyls, caboxylates, esters, hydroxyls , sulfhydryls and the like. Examples of directed energy include atmospheric corona discharge, radio frequency (RF) vacuum plasma treatment, and DC glow discharge. These polymer surface treatment methods have displayed varying degrees of success and their effects tend to decay overtime.
In the case of plasma treatment, plasmas are created when a sufficient amount of energy, is added to gaseous atoms and/or molecules, causing ionization and subsequently generating free electrons, photons, free radicals, and ionic species. The excitation energy supplied to a gas to form a cold plasma can originate from electrical discharges, direct currents, low frequencies, radio frequencies, microwaves or other forms of electromagnetic radiation. Plasma treatments are common for surface modification in the microelectronic and semiconductor industries. As mentioned, atmospheric corona and RF plasma treatment are commonly used for polymeric surface activation for cell growth substrates as well as medical implants.
Current standard practices for growing adherent cells in cell culture involves the use of defined chemical media to which is added up to 10% volume bovine or other animal serum. The added serum provides additional nutrients and/or growth promoters. In addition serum proteins promote cell adhesion by coating the treated plastic surface with a biolayer matrix to which cells can better adhere. The addition of serum is typically required to support the normal growth of the majority of cell lines. While advantageous for cell growth, serum can have adverse effects by intruding sources of infection or abnormally inducing expression of unwanted genes exposed to serum.
According to the present invention, a stream of plasma is comprised of activated gaseous species generated by a microwave source. This stream is directed at the surface of a polymer substrate in a controlled fashion such that the surface is imparted with attributes for cell adhesion far superior to that of untreated polymer or polymer treated by other known methods. The treatment apparatus contains a microwave generator and gas line feeding into a plasma mixing chamber. The plasma mixing chamber is connected to a dual chambered treatment chamber, comprising an inner chamber and an outer chamber. The outer chamber connects directly to the plasma mixing chamber and has a vacuum line outlet in order to create a plasma flow. The inner chamber is contained within the outer chamber and contains a baffle that directs the plasma flow directly onto the polymer surface which is to be treated. The part that has been subjected to the directed plasma stream is imparted with uniform surface characteristics that enable extraordinary levels of cell attachment even under reduced serum conditions. It will be obvious to one skilled in the art that this surface may also be advantageous in protein binding assays.